The present invention relates to fluid coupling devices, and more particularly, to such devices which include a temperature responsive bimetal element to control the operation of the fluid coupling in response to changes in ambient air temperature.
Although the present invention may be used advantageously in fluid coupling devices having various configurations and applications, it is especially advantageous in a coupling device of the type used to drive the radiator cooling fan of an internal combustion engine, and will be described in connection therewith.
A fluid coupling device of the type to which the present invention relates typically includes an input coupling member and an output coupling member. The output coupling member cooperates with a cover assembly to define a fluid chamber and a valve plate separates the chamber into a reservoir chamber and an operating chamber. The input coupling member is rotatably disposed within the operating chamber, and cooperates with the output coupling member to define a viscous shear space such that torque may be transmitted from the input member to the output member by means of a viscous shear fluid.
The valve plate typically includes a valving arrangement operable in response to variations in ambient air temperature to permit fluid to flow from the reservoir chamber, through a fill opening defined by the valve plate, into the operating chamber. Conventionally, the valving arrangement includes a valve member which covers or uncovers the fill opening in response to movement of a temperature-responsive bimetal element, which senses variations in the ambient air temperature.
Among the trends in the automotive and light truck industry has been the increasing percentage of vehicles equipped with air conditioning. In a typical vehicle installation, the air conditioning compressor, which must dissipate a substantial amount of heat, is cooled by air in the engine compartment, i.e., the same air which is drawn through the radiator to cool the engine coolant. Thus, when the ambient air surrounding the viscous fan drive reaches a predetermined temperature, the bimetal on the fan drive will actuate the valving and the fan drive will operate in its engaged condition. When this occurs, the viscous fan drive rotates the radiator cooling fan, pulling air through the radiator to cool not only the engine coolant but also the air conditioning compressor.
Unfortunately, it frequently occurs that the air conditioning compressor is operating, and requires cooling, in a situation in which the ambient air surrounding the viscous fan drive is below the predetermined temperature at which the fan drive would normally engage. Therefore, the fan drive continues to be in the disengaged mode, because of the relatively low ambient air temperature, but unless cooling is provided for the air conditioning condenser, it is possible the air conditioning system will not operate properly.
There are also certain vehicle applications for viscous fan drives in which the vehicle OEM chooses to have the viscous fan drive operate in a disengaged mode at relatively high engine speeds, when the "ram" air passing through the radiator is sufficient for cooling purposes, without the need for operation of the radiator cooling fan. Typically, in such situations, the ambient air temperature does not drop to a low enough temperature to cause disengagement of the viscous fan drive, even though its operation in the engaged mode is not really required. Continued operation of the fan drive in such situations represents a waste of engine horsepower.